Comfort is a relative term that is different for virtually every individual because of sex, age, ethnicity, and activity level. Comfort is tied not only to the temperature but also to the relative humidity of an environment. Scientists have also found that a humidity level between 30 and 50 percent discourages many types of mold, dust mites, allergens, and certain bacteria.
There have been air conditioning and heating systems designed to remove humidity from the air. Many of these depended on reheating the cooled air either by use of additional heat from the oil or gas furnace or electric heat, both of which are cost prohibitive. Other approaches have included multiple evaporators and condensers but these were often difficult to control and required complex controls both for the temperature and the storage of refrigerant. A more common method of removing humidity is by adding a separate dehumidifier to the system which is often cost prohibitive plus duplicates the refrigeration system in the air conditioner or heat pump.
There have also been attempts to reduce humidity by extending the cooling cycle after the thermostat has reached the preset cooling temperature. This is normally in conjunction with a reduction in the fan speed of the air handler motor. The reduction in fan air volume reduces the heating effect of the air passing over the evaporator which in turn lowers the temperature of the evaporator. The temperature reduction will be lowered to below the dew point temperature of the air and moisture from the air will condense on the coil thus reducing the humidity level of the space. The current designs typically allow the temperature to be reduced below the set point of the thermostat by a preset amount thus cooling the space below that was desired. When the final temperature is reached, the unit will shut off and will not restart until cooling is called for. If the temperature inside the structure stays below the set point of the thermostat cooling is not called for and the humidity level can rise above the comfort level. This is the “clammy” or damp feeling often encountered in the Spring and Fall of the year space is often described as feeling “clammy”.
Requirements by the United States government have dictated that the efficiency of air conditioning equipment and heat pumps must meet or exceed a Seasonal Energy Efficiency Rating (SEER) of 13 by January, 2006. Many of the manufacturers of air conditioning equipment have achieved this goal by increasing the size of both the evaporator and the condenser coils. This lowers the pressure differential across the compressor which results in less power consumption per BTU (British Thermal Unit). The increased size of the evaporator has reduced the ability of the air conditioning system to remove moisture from the air resulting in higher humidity levels. There are no federal energy savings requirements for dehumidifiers.